One day I'm sure vmware will update their documentation online to match the 5.3 product. However google helped me find this document:
http://www.vmware.com/pdf/horizon-view/horizon-view-html-access-document.pdf
Page 16 describes the group policy setting "Configure Clipboard Redirection"
Set it to "Enabled in Both Directions".
You have to copy the group policy template file from one of your Guests with the feature pack installed.
I can confirm that this works as described. You get copy / paste in both directions. You also get a message when you copy in the guest informing you how to copy the data back through the HTML5 client.
